Current art semiconductor device manufacturing technology utilizes positive photoresist materials to photolithographically delineate patterns on substrates. These patterns are etched by wet or dry etching techniques later in the manufacturing process and are either left permanently or removed during processing. One class of machines used in etching these patterns are plasma etching systems. Several manufacturers in the United States, Japan, and Europe manufacture them. Commercially available systems include the Applied Material 5000, the Lam Rainbow etchers, the Tegal plasma etchers, Anelva etchers, and others.
The photoresist patterns can be etched with different mixtures of organic and inorganic chemicals. The systems used for the wet etching are called Wet-Benches. Several manufacturers manufacture these wet-benches made of Polypropylene, Teflon, and sometimes Stainless Steel. The chemical mixtures used are Sulfuric Acid, Hydrofluoric Acid, Acetic Acid, and the like. Sometimes these acid mixtures are used at room temperature, and sometimes they are heated from 25.degree. C.-160.degree. C. The positive photoresist materials are spun onto substrates or are otherwise applied to substrates.
The substrates are then exposed to UV light utilizing different types of exposure machines. After exposure, the substrates are subjected to a development process where, due to selective dissolution of certain areas of the photoresist, a pattern is developed. The resist in certain areas is completely removed by this process step. In certain other areas, resist is left behind to protect the underlying metal or dielectric films.
The resist layer may then be exposed to deep UV blanket light or baked at high temperatures in order to stabilize the resist, which enables the resist to withstand the plasma etching process. The blanket UV exposure also improves the aspect ratio of etching metal or dielectric and the photoresist. The baking temperatures may range from 90.degree. C. to 250.degree. C. for from 30 seconds to 120 seconds. This treatment improves resist selectivity and provides better etching and dimensional controls of etched patterns. It also enables engineers to go up to and more than 200% over etch in order to ensure that desired etching material, whether it is a metal or a dielectric film, is completely gone from the area and no traces are left behind in between patterned lines or inside holes.
The remaining photoresist material is then further exposed to dry etching or wet etching procedures as required by the manufacturing process. The etching process is essential to define the patterns and leave behind under the photoresist pattern the metal or dielectric film, oxide, poly or other insulator film. The underlying layer is utilized later in the process of manufacturing semiconductor chips.
It is necessary in such full lithographic processes to ensure that the photoresist material, following pattern delineation, is evenly and completely removed from all unexposed areas of the substrate so as to permit further operations. Even minute traces remaining of the photoresist material or resist coating in an area to be further processed are highly undesirable. Residue of the photoresist material or resist coating can have a detrimental yield impact.
The objective of the plasma etching processes or wet etching process is to remove metal films such as Titanium, Titanium-Tungsten alloy, Aluminum, Aluminum Silicon Copper alloy, Titanium Nitride films, or Spin on glass films, BPSG (Borophosphate silicate glass) films, or films of a similar nature, that a thin film on the sides of the patterns is redeposited as either a metal line or a hole in the dielectric film. These redeposit films are identified by many different names, such as metal veils, side wall polymers, passivation polymers, photoresist polymers, via veils, via polymers, fences, tulips, etc. The redeposit films are organometallic residues that are formed and redeposited onto the substrates. These residual polymers are hard, and are very difficult to remove by conventional strippers or oxygen plasma. One reason that removal of the residual polymers is difficult is that it is very important that the photoresist stripper does not attack nor make a slight change on the exposed metal lines or via hole sidewalls. The photoresist stripper should remove all resist as well as polymer from the substrate.
Conventional resist strippers or polymer removers available on the market are typically made with either Hydroxyl Amine, Pyrollidone, Glycol ethers, Dimethyl sulfides, or ethanol. Other types of Acid mixtures, such as sulfuric acid heated to 120.degree. C. and added to approximately 200-500 ML of hydrogen peroxide to create a strong oxidizing agent, are used to strip resists from substrates. This type of mixture can only be used prior to the deposition of any metal layer, because the mixture can strip all the metal from the substrate. If the sulfuric acid/hydrogen peroxide mixture is used on substrate with metal applied, the metal may be stripped from the substrate, which can require that the substrate be scrapped. This can be a significant financial loss for the manufacturer.
The prior art resist strippers and polymer removers are all subject to some drawbacks. HDA-based strippers/polymer removers have limited effective temperature operating ranges. If the chemical temperature is raised above 65.degree. C., the stripper attacks underlying metals, such as Titanium, Nickel, Titanium Nitride, Aluminum and the like, causing manufacturing defects.
HDA types of chemistry are subject to the drawback of attacking SOG (spin on glass) films, especially SOG films which have low dielectric constants. Another drawback of HDA formulations are their evaporation rate. Further, HDA chemistries are very toxic. Disposal is therefore very expensive.
Another type of chemicals used for stripping purposes are mixtures of Anhydrous Ammonium fluorides in Ethylene Glycols. These mixtures pose the dangers of attacking SOG severely and also attacking metal films of the types mentioned above. The mixtures include Hydrofluoric Acid, thus requiring the use of hazardous waste disposal techniques.
Accordingly, it is an object of the present invention to provide stripping formulation a that effectively removes photoresist material or resist coating.
It is a further object of the present invention to provide a stripping formulation that does not attack SOG or metal films.
It is a still further object of the present invention to provide a stripping formulation that is not highly toxic so that it can be disposed of easily.